Printed dipole antennas that include a pair of straight conducting strips on a printed circuit substrate are known in the art. The substrate can be, for instance, a material such as FR4, GETEK, DUROID or TEFLON. The dipoles in these prior antennas typically are a half-wavelength long, and are characterized by a radiation resistance of between 50 to 70, depending on substrate thickness, dielectric constant of the substrate, and the width of the metal strips of the antennas.
A problem arises with such antennas when used in applications with restrictive size constraints, since the length of the dipole may be unacceptably long. For example, in a 900 MHz application, half the wavelength is approximately 16 cm. The size of an antenna having this length is prohibitively large for many applications.
One solution to this problem that has been proposed is to shorten the dipole length. The result of this solution, however, is an antenna having a very low radiation resistance, and which does not resonate. Further, the efficiency of such small antennas is extremely poor.
Clearly, as the need for compact, efficient antennas increases, an improved antenna design is required.